The case of an 83-year old woman with a history of thyroid cancer, breast cancer, and rheumatoid arthritis is presented. She had no relevant family history. After surgery for thyroid and breast cancers, elevations of carcinoembryonic antigen and carbohydrate antigen 19-9 were observed. She had no abdominal tenderness, and no mass was palpable. Laboratory results were unremarkable. Colonoscopy showed a type 2 tumor localized in the upper rectum. Following biopsy, the lesion was confirmed to be moderately differentiated adenocarcinoma. Contrast CT examination showed wall thickening of rectal cancer and swollen lymph nodes, but there were no distant metastases. In addition, abdominal contrast CT examination also revealed vascular anomaly. Laparoscopic surgery was planned, and a 3D-CT was constructed from contrast CT images to investigate local vascularity. The 3D-CT scan showed a venous malformation forming a short circuit (Retzius shunt) from the IMV to the IVC. Based on these findings, upper rectal cancer with a Retzius shunt from the IMV to the IVC was diagnosed. Laparoscopic anterior resection was performed. Laparoscopic observation showed a number of engorged vessels in the mesentery and the Retzius vein crossing the abdominal aorta and inferior mesenteric artery (IMA) to the IVC. The Retzius vein and IMA were clipped without major bleeding, and then tumor-specific mesorectal excision was completed. The patient was discharged on the 14th day after surgery with no complications. Histological examination showed the tumor to be moderately differentiated adenocarcinoma with invasion of the subserosa (T3) and lymph node metastasis (N2). No distant metastases were found (M0) at the time of surgery. The histological TNM staging of the tumor was stage IIIB, with no other remarkable findings.